1. Field of Art
This invention relates to a novel precursor of a silicon-containing polyimide polymer, a method for preparing the same, and a use of the same.
As protective and insulating materials in the field of electronics, polyimide resins have been widely used mainly from the viewpoint of their heat-resisting properties. From the overall point of view, however, they are not always satisfactory in this field with not a few points to be improved. In general, a precursor of polyimide for electronic materials is coated, in the form of a polyamic acid solution, on a base material, and baked to form a cured imide product. Such a coating solution has extremely high viscosity, leading to a drawback of poor workability. Furthermore, such a precursor has other drawbacks that baking thereof requires so high temperatures, e.g., 300.degree. to 400.degree. C., so as to exceed the temperature of heat resistance of the base material, and that adhesion thereof to an object to be coated therewith, such as a silicon wafer or glass, is insufficient.
2. Prior Arts
A number of copolymers of polyimide precursors with silicon compounds have been proposed for the improvement of adhesion. For example, Japanese Patent Application Laid-Open Specifications No. 143,328 (1982), No. 7,473 (1983) and No. 13,631 (1983) have proposed polyimidesiloxane copolymers which are obtained by replacing a part of a diamine as a raw material with a polysiloxane terminated with diamine molecules at both the ends thereof. However, this case involves drawbacks that the heat-resisting properties of cured products formed from these copolymers are reduced with increasing siloxane contents in the copolymers, and that copolymerization of the diamine with the polysiloxane entails lowering of the polymerization degree of the resulting polyamic acid, leading to poor film forming properties.
Japanese Patent Publications No. 32,162 (1983), and No. 32,163 (1983) disclose polyamide carboxylic acids and the like including amic acids usable in the present invention. However, these polyamide carboxylic acids and the like have a drawback that baking thereof into imides requires high temperature of at least 300.degree. C. as in the case of conventional polyamide carboxylic acids. These pieces of patent literature further disclose cyclization (imide formation) carried out chemically by a treatment with a dehydrating agent under mild condition. However, the cyclization according to this treatment requires a long time, and the resultant cyclized products have a drawback that those having Si contents are inferior in film forming properties due to low viscosities in the form of varnishes thereof attributed to low molecular weights thereof, while those having low Si contents are inferior in adhesion of cured products therefrom to a silicon wafer or glass.
It is, therefore, an object of the present invention to provide a polyimide-siloxane prepolymer which are suitable for use in surface protecting films for semiconductors and in insulating films between multi-layer wiring layers, soluble in an adequate solvent, capable of being cured by baking at relatively low temperature, which provides good workability when made into a solution and good film-forming properties, and which provides good adhesion of a cured product therefrom to a silicon wafer, glass, and the like.